Hydraulic buffers

ABSTRACT

A hydraulic buffer device of the type in which a piston is slidable in a cylinder and has a throttle aperture which is controlled by a regulating pin whose cross section varies along its length. The throttle aperture is closable by a valve member which is spring loaded into the closing position. On rapid entry of the piston into the cylinder the valve member is unsealed and a relatively low resistance to piston travel is afforded. On slow entry of the piston into the cylinder the valve member remains seated and a relatively high resistance to travel of the piston is afforded.

United States Patent Zielinski Dec. 18, 1973 [54] HYDRAULIC BUFFERS3,411,635 11/1968 Powell 213/8 3,160,285 12/1964 Sinclair et a1 213/43[751 6mm", Germany 3,164,263 1/1965 Novikov et al. 213/43 [73] Assignee:Rheinmetall GmbH, Dusseldorf,

Germany Primary Examiner-Drayton E. Hoffman [22] Filed: Man 30, 1972Attorney-Paul M Craig, Jr. et al.

App]. No.: 239,668

Foreign Application Priority Data Apr. 17, 1971 US. Cl 213/43, 213/223,267/65 R Int. Cl. B6lg 9/08 Field of Search 213/8, 43, 223;

References Cited UNITED STATES PATENTS 7/1964 Thornhill ..2l3/43 9/1968Powell ..2l3/8 Germany P 21 1s 655 0 [57] ABSTRACT A hydraulic bufferdevice of the type in which a piston is slidable in a cylinder and has athrottle aperture which is controlled by a regulating pin whose crosssection varies along its length. The throttle aperture is closable by avalve member which is spring loaded into theclosing position. On rapidentry of the piston into the cylinder the valve member-is unsealed and arelatively low resistance to piston travel is afforded.

On slow entry of the piston into the cylinder the valve member remainsseated and a relatively high resistance to travel of the piston isafforded.

2 Claims, 5 Drawing Figures mgmmnia 18 m5 SHEET 2 OF 3 HYDRAULIC BUFFERSis suitable for withstanding impacts during shunting operations. In thiscase the piston has a relatively high entry speed and it is necessary toabsorb these impacts so that the energy is dissipated, in order to avoidhigh decelerations or accelerations of the carriages and goods.

However, during the travel of a railway train, as well as duringbraking, only slight differences in speed occur between the individualcarriages so that the buffer piston enters the cylinder at a relativelylow speed.

With the known hydraulic bufiers of the type described above this wouldhave the result that on braking the train the coupling would be severelycompressed, due to which when the train moves off again or when thebrakes are released, undesirable, alternating pulling and pushingmovements between the carriages and in particular during rapid brakingof long trains high longitudinal forces occur. Therefore, fortravelling, a coupling which is as rigid as possible is desired, whichwith low entry speeds of the buffer piston produces a considerablebuffer force.

It is an object of the invention to provide a hydraulic buffer devicefor vehicles, in particular rail vehicles, which with low piston entryspeeds as they occur between the individual carriages when braking atrain has a high resistance and in the case of impacts causing higherpiston entry speeds has a comparatively low resistance, the hydraulicbuffer force being determined solely by the piston entry speed and thecolliding masses.

In a hydraulic buffer device of the afore-described type, this object isfulfilled according to the invention in that an annular valve coneslidably guided on the regulating pin and supported on the latteragainst a closing spring is associated with the throttle apertureprovided concentrically in the piston, as a pressure limiting valve.

When the train is standing still, and with low piston entry speeds, suchas occur at the buffer when slowing down the train, the throttleaperture remains closed due to the valve cone, which thus forms alocking device and produces a comparatively rigid coupling of the train.Only when a pressure corresponding to the initial stressing force hasbuilt up in the cylinder in frontof the piston is the valve cone pushedback against the force of its closing spring and the throttle aperturecleared. Thus in the case of low piston entry speeds the valve coneclosing the throttle aperture determines the buffer force. In the caseof high entry speeds, such as occur during forceful impacts, the valvecone is not able to follow the leading piston at the same speed, so thatthe annular throttle opening is cleared.

In a preferred embodiment of the invention the valve cone is located atone end of a sleeve guided on a cylindrical section of the regulatingpin, the other end of which sleeve forms an annular cylinder chamberwith a section of lesser diameter adjoining the cylindrical section, thewall of which chamber has a throttle bore.

The closing speed of the valve cone is determined according to thedimensions of the throttle bore, in that the pressure fluid located inthe cylinder chamber has to be pushed through the throttle bore by theforce of the valve spring. I

The load characteristic of the closing spring of the valve cone is inthis case appropriately arranged so that in the case of low entry speedsdepending on the buffer stroke an approximately constant buffer forceresults. In cooperation with the mechanical spring of amechanical/hydraulic buffer and draw gear device a force pattern of thistype results in the buffer force of the mechanical spring increasing asthe piston enters the buffer, whereas the spring force of the closingspring of the pressure limiting valve is reduced and thus due to theopening of the valve the fluid pressure in the buffer cylinder isreduced.

The invention will now be further described with reference to theaccompanying drawings, in which:

FIGS. 1-3 show a buffer and draw gear device for central buffercouplings with one embodiment of hydraulic buffer device according tothe invention shown in longitudinal section, in various positions.

FIGS. 4 and 5 show the hydraulic buffer device in various positions ofthe buffer piston in longitudinal section as a partial section of FIG. 1on an enlarged scale.

Whereas FIG. 3 shows a mechanical hydraulic buffer and draw gear devicein the starting position, FIG. 1 shows the device in the pushingposition in the case of impact and FIG. 2 shows it in the pullingposition. The reference numeral 1 indicates the housing of the bufferand draw gear device forming a closed unit. The housing consists of thecup-shaped part In receiving the hydraulic part, an adjoining sleeve 1band a support sleeve 1c serving for supporting the mechanical spring.The unit is rigidly secured to a carriage on the longitudinal centralaxis thereof. A moving part 2 of the device is located in the housing.The device has, at its end projecting from the housing, a coupling part3 for the flexible attachment of the central buffer coupling and, at itsother end, a piston rod 4a with a buffer piston 4, which projects into ahydraulic cylinder 5 formed in the cup-shaped part la.

The mechanical spring mechanism comprises two annular spring columns 6and 7 arranged concentrically around the moving part 2. The outerannular spring column 6 is fixed between an annular flange 3 secured tothe movable part 2 of the device and a shoulder 9 of a sleeve 10 movablerelative to the movable part 2. The inner annular spring column 7 isfixed between an annular flange 11 secured to the sleeve 10 and a collar12 of a sleeve 13, which is slidably guided on a boss 14, which islocated on a removable end wall 15 of the cylinder.

A regulating pin 17 is secured in an end wall 16 of the cylinderopposite the piston 41 and extends through a central throttle aperture18 in the piston into a hollow piston rod 4a. Starting from the end wall16 of the cylinder the regulating pin has, firstly, a section 19 oftapering diameter, a cylindrical section 20 of greater diameter and acylindrical section 21 of lesser diameter. The diameter of the throttleaperture 18 is such that a narrow annular clearance remains between itand the periphery of the cylindrical section 20 (FIGS. 4 and 5).

A sleeve 22 of substantially greater length than that of the section isguided on the cylindrical section 20, which sleeve has at one end avalve cone 23 and at its other end a shoulder 25 guided on the section21 of lesser diameter forming an annular cylinder chamber 24. A throttlebore 26 is provided in the wall of the cylinder chamber. The sleeve 22with the valve cone 23 is supported against a spring washer 28 by a coilspring 27 acting as a closing spring, which spring washer 28 is attachedto the end of the cylindrical section 21 of the regulating pin. Theclosing speed of the valve 23 depends on the load characteristic of theclosing spring and the cross section of the throttle bore 26 in the wallof the cylinder chamber 24. In this way, the valve cone 23 forms apressure limiting valve for the pressure fluid located in the hydrauliccylinder 5, which can pass when the valve is open through the throttleaperture 18 and through bores 29 located in the piston 4 to the otherside of the piston, the cylinder space being connected by way ofapertures 30 to a compensating chamber 31 surrounding the cylinder. Abore 33 closed by a resilient valve plate 32 is also provided in thefront end of the piston.

The compensating chamber 31 does not work as a hydropneumatic pressurereservoir, its function is solely to receive the fluid displaced by thepiston rod at the time of the pushing stroke or to supply the additionalamount of fluid required at the time of the pulling stroke and tocompensate for changes in volume caused by heating.

The method of operation of the mechanical/hydraulic buffer and draw geardevice is as follows:

FIG. 3 shows the device in the starting position. This positioncorresponds to the position of the buffer piston illustrated on a largerscale in the lower half of FIG. 4.

The pressure limiting valve is closed and, apart from their prestress,the annular spring columns are unloaded. Under tensile load (FIG. 2) theouter annular spring column 6 is compressed, it being supported againstthe carriage construction by means of the support sleeve 10, whereas theinner spring column 7 is only displaced by the same amount. The piston 4also moves by the same amount (FIG. 5 at the top), the valve 23remaining closed and the valve plate 32 lifting so that the pressurefluid is able to pass through the bore 33 into the space in front of thepiston 4. Simultaneously, the cylinder chamber 24 formed between thewall of the sleeve 22 and the section 21 of the regulating pin is filledthrough the throttle bore 26. FIG. 2 shows the extreme position at thetime of the greatest tensile load. During the travel of a railway trainthe device will adopt a position corresponding approximately to FIG. 3and FIG. 5 at the bottom.

At the time of braking the train only slight differences in speed occurbetween the individual carriages and thus the entry speed of the bufferpiston is low. In this case the spring mechanism assumes the positionshown in FIG. 1 and in FIG. 5 at the top. Since, in this case, thebuffer piston 4 enters the cylinder at a comparatively low speed,sufficient time remains for the pressure fluid located in the cylinderchamber 24 to be displaced through the throttle bore 26 under the actionof the force of the closing spring 27, so that the throttle opening 18remains closed by the valve cone 23. In this way the mechanical springmechanism is, as it were, locked during travel and at the time ofbraking the train, so that during these operating conditions the bufferand draw gear device has a high initial stressing force.

In the case of greater dynamic loads, as they occur with impacts, thebuffer piston is inserted into the cylinder at a comparatively greaterspeed (FIG. 1). The valve cone 23 actuated by its closing spring 27 isnot able to follow the rapid movement of the piston, since for this thefluid located in the cylinder chamber 24 must be pushed out through thethrottle bore 26. In consequence and aided by the pressure build-up infront of the piston 4, the valve opens, so that the fluid can passunhindered through the throttle aperture 18 to the other side of thepiston. Thus, in the case of dynamic loading with a certain range ofpiston speeds, the hydraulic buffer device has a lower resistance sothat even with impacts between lighter carriages no greater accelerationor deceleration values occur.

What is claimed is:

1. Hydraulic buffer device comprising: a cylinder, a piston slidable insaid cylinder, a throttle aperture provided in said piston, a regulatingpin for varying the available cross-section of said throttle aperture,said regulating pin being provided with a cross-section which varies inthe longitudinal direction of said cylinder, a sleeve guided on acylindrical section of said regulating pin, a slidably guided annularvalve member disposed on one end of said sleeve, an annular cylinderchamber formed by the other end of said sleeve, said annular cylinderchamber being provided with a section of a lesser diameter adjoining theguide end of said sleeve, spring means for biasing said annular memberto close said throttle aperture in said piston, and a throttle boreprovided in a wall of said annular cylinder chamber for determining theclosing speed of said annular valve member.

2. Hydraulic buffer device according to claim 1 further comprising: amechanical buffer and draw gear device, wherein the load characteristicsof said spring means and said mechanical buffer are selected to achievean approximately constant buffer force.

1. Hydraulic buffer device comprising: a cylinder, a piston slidable insaid cylinder, a throttle aperture provided in said piston, a regulatingpin for varying the available cross-section of said throttle aperture,said regulating pin being provided with a cross-section which varies inthe longitudinal direction of said cylinder, a sleeve guided on acylindrical section of said regulating pin, a slidably guided annularvalve member disposed on one end of said sleeve, an annular cylinderchamber formed by the other end of said sleeve, said annular cylinderchamber being provided with a section of a lesser diameter adjoining theguide end of said sleeve, spring means for biasing said annular memberto close said throttle aperture in said piston, and a throttle boreprovided in a wall of said annular cylinder chamber for determining theclosing speed of said annular valve member.
 2. Hydraulic buffer deviceaccording to claim 1 further comprising: a mechanical buffer and drawgear device, wherein the load characteristics of said spring means andsaid mechanical buffer are selected to achieve an approximately constantbuffer force.